Dynamoelectric machines conventionally include stacks of laminations made up of magnetic material as part of their rotor construction. In many cases, heat is generated in the lamination stack as a result of eddy currents induced by magnetic fields generated during operation of the machine or as a result of hysterisis losses. If the rotor is provided with an electrical winding, the lamination stack may be heated as a result of heat transfer from electrical windings which in turn heat up during the operation of the machine as a result of I.sup.2 R losses. Over the years, many efforts have been made to prevent lamination stacks of the sort mentioned above from overheating. For example, the use of stacks of laminations itself is employed to reduce eddy current losses which in turn reduces the heat generated in the rotor. Moreover, it is common to include a fan on the motor shaft for drawing or propelling the coolant, typically ambient air, across machine components including the lamination stack.
It has also been conventional to provide coolant passages in the lamination stack and flow a coolant that may range from ambient air to oil to a refrigerant through such passages for cooling purposes. While such schemes have worked well for their intended purpose, energy must be expended to flow an adequate amount of coolant through the coolant passageways to prevent undesirably high temperatures from being attained. The energy used for this purpose lowers the overall efficiency of the machine. Moreover, as the coolant passages are inherently characterized by the lack of magnetic material in the cross section of the coolant passage, magnetic inefficiency may result which in turn may require the use of a somewhat larger rotor to prevent undesirable magnetic saturation occurring in parts of the rotor whereat coolant passages are located. The greater rotor mass also leads to operational inefficiencies.
Consequently, there is a real need for a dynamoelectric machine having a rotor wherein eddy current losses are further reduced and wherein the rotor may be adequately cooled without interfering with magnetic flux in the rotor during operation of the machine incorporating the rotor. The present invention is directed to providing a rotor with reduced eddy current losses and improved cooling without disrupting the magnetic efficiency of the rotor to provide an overall increase in the efficiency of operation of the dynamoelectric machine.